Flotation apparatus for supporting loads are currently in wide use, and are commonly used as beds for human beings. The most common type of water bed is essentially a vinyl envelope filled with water and placed within a frame. This basic design has many disadvantages, one of which is its great weight due to the large volume of water necessary to fill the envelope to a depth sufficient for comfortably supporting the weight of one or more human being. Such a device or mattress must hold fluid approximately nine inches deep and weighs approximately forty pounds per square foot exclusive of the base and frame which must be used in conjunction with it. The frame is necessary because without it the sides of the envelope will assume a rounded shape reducing the amount of support available near the edges, and allowing a user to roll off the curve.
This type of mattress has a number of disadvantages, not the least of which is the difficulty of using standard bedding such as sheets and mattress covers. Fitted sheets for example, cannot be placed around the corners of the envelope because of its weight and size. Non-fitted sheets cannot be tucked under the heavy envelope, and therefore have a tendency to slide on the surface of the mattress.
Another major disadvantage with this type of construction is that waves are created as movement occurs on the mattress, and these waves are reflected by the walls of the rigid frame, creating nodes which can be quite severe and which continue reflecting themselves throughout the mattress for a considerable length of time.
Furthermore, and most importantly, such a mattress is not capable of being easily adjusted to alter the supportive force provided. If the water pressure is raised in an attempt to increase the firmness of the mattress, then the therapeutic advantages of the water are lost and comfort is decreased because the body no longer floats on the liquid, but rather is supported by tension in the envelope.
These types of mattresses have a short life span because the forces exerted at the seams by the substantial amount of water contained in the envelope cause rupture and leakage.
In order to avoid some of these disadvantages, a number of alternative designs have been developed over the years. In order to reduce the wave action within the mattress, baffles have been added to slow the movement of the wave forces. However, because the baffles are thin and essentially non-compressible, the wave forces are transmitted through the baffles from one chamber to the next, and thus have only a small effect on the wave action.
Another design includes the use of air chambers under the envelope of water. The air chambers, because they provide a supportive force of their own, allow a reduction of the depth of water required. Consequently, some of the wave action is reduced and the firmness of the mattress can be more easily modified by changing the air pressure in the air chamber. However, the balance of the disadvantages as discussed above are not eliminated.
Another alternative design is to use a resilient foam slab under or in the water filled envelope in place of the air chamber. However, such a mattress is not adjustable by the user to change the supportive force.
Accordingly, the principal objects of the present invention are to provide a flotation apparatus which requires much less liquid than the present devices, which can be used with standard bedding, and, most importantly, which is easily adjustable to suit the needs of the user while providing optimum buoyant support over its entire surface area.